The present invention relates to a fuel tank arrangement for dual fuel internal combustion engine of a vehicle. The invention also relates to a vehicle comprising such a fuel tank arrangement. The invention is applicable on vehicles, in particularly low, medium and heavy duty vehicles commonly referred to as trucks. Although the invention will mainly be described in relation to a truck, it may also be applicable for other type of vehicles such as e.g. working machines, cars, etc.
In relation to propulsion systems for vehicles, such as heavy duty vehicles, internal combustion engines are frequently used. These internal combustion engines are most often propelled by a combustible fuel such as e.g. diesel or petrol. However, in order to further reduce engine emissions of the vehicles, alternative propulsion methods and/or fuels are being used, either alone or in combination with the well known combustible fuels. These may include, for example, ethanol or electrical propulsion from an electric machine, etc.
As a further alternative, a combustible gas, such as e.g. compressed or liquefied natural gas, DME, biogas, etc. has been found a suitable propulsion fuel for vehicles in the form of trucks. The combustible gas can be used in combination with the combustible fuel for propelling the internal combustion engine, in the following referred to as a dual fuel internal combustion engine. Since the residuals from the combustible gas are relatively environmentally friendly in comparison to e.g. combustible fuels, pollution from the emissions may be reduced for these types of engines.
However, for the above described dual fuel internal combustion engines there is a risk that combustible gas can leak from the engine back to the diesel tank. Combustible gas is in these cases mixed with the combustible fuel in the fuel tank and there is a risk that the gases leak to the ambient environment therefrom.
US 2012/0325180 relates to a method for operating an electrically controlled dual fuel compression ignition engine. US 2012/0325180 describes a natural gas tank connected to a gas fuel common rail, and a file tank which is connected, to a liquid fuel common rail. Natural gas and liquid fuel are mixed in a coaxial quill assembly before being provided into the cylinders of the engine. Furthermore, a drain outlet is fluidly connected to the fuel tank to drain fuel from the injectors to the fuel tank. However, US 2012/0325180 is still in need of further development with regards to handling of gases in case of leakage.
Furthermore, US 2010/0083938 relates to a marine carbon canister. In detail, US 2010/0083938 relates to a fuel tank vent system that includes a carbon canister. Fuel vapor discharged from the fuel tank included in the engine fuel system flows during certain conditions into the carbon canister to encounter charcoal stored in the carbon canister.
It is desirable to provide a fuel tank arrangement which at least partially overcomes the deficiencies of the prior art.
According to a first aspect of the present invention, there is provided a fuel tank arrangement for a dual fuel internal combustion engine, the fuel tank arrangement comprising a fuel tank arranged to supply liquid fuel to the dual fuel internal combustion engine, wherein the fuel tank arrangement comprises a return conduit connected to the fuel tank and configured to supply leaked fuel from the dual fuel internal combustion engine to the fuel tank, wherein the fuel tank arrangement comprises a first fuel separation arrangement positioned in fluid communication between the fuel tank and an outlet to an ambient environment thereof.
A dual fuel internal combustion engine should be understood to mean a combustion engine which can be propelled by both a combustible gas and a combustible fuel, or a mixture thereof. The combustible fuel may, for example, be diesel or petrol. However, the present invention should not be construed as limited to any specific alternative.
Furthermore, a fuel separation arrangement should be understood to mean an arrangement which is able to separate liquids from gases, or vice versa, which will be described further below. Still further the wording “fluid communication” should in the following and throughout the description be interpreted as valid for fluids in liquid phase as well as in gas phase.
When combustible gas ends up in the fuel tank, there is an increase in pressure therein which is in need of ventilation. The ventilation may thus be necessary in order to avoid e.g. burst of the tank. An advantage of the present invention is thus that combustible gases which have accidentally leaked from the dual fuel internal combustion engine into the fuel tank can be separated from the combustible fuel during venting. Hereby, the combustible fuel can, by means of the first fuel separation arrangement, be returned to e.g. the fuel tank, while the combustible gas, which is relatively free from mixture with combustible fuel, can be directed towards the ambient environment of the vehicle. It is thus a reduced risk of spilling liquid fuel. As an example, it may be beneficial to vent the combustible gas at the top of a so-called vent stack of the vehicle, which is positioned above the chassis department of the vehicle. An advantage is thus that the combustible gases will be vented at a position which is free from inhalation since the density of the combustible gas is lower than air and will thus rise from a relatively high position. A further advantage of venting the combustible gas at the relatively high position of the vehicle is that there is a reduced risk of gas ignition since the environment at the vent stack is free from high temperature vehicle components.
Furthermore, throughout the entire description of the application, the wordings “above” and “below” should be understood to relate to a vertical direction of the vehicle. The vertical direction should be seen in relation to a vehicle standing on a relatively flat/horizontal surface. Likewise, the wordings “upper” and “lower” should also be understood to relate to a vertical direction of the vehicle.
According to an example embodiment, the fuel tank arrangement may comprise a gas tank arranged to supply combustible gas to the dual fuel internal combustion engine.
The wording “combustible gas” should in the following and throughout the entire description be interpreted as a gas which can be ignited, either self-ignited by compression or be ignited by e.g. a spark plug. The invention should thus not be limited to any specific combustible gas. However, as a non-limiting example, the combustible gas may be natural gas, which is described further below. Other alternatives are of course conceivable such as e.g. H2, DME, biogas, gaseous hydrocarbons, etc. The combustible gas which can be provided in the gas tank can be in liquid phase and in gas phase. Hence, the wording “combustible gas” should be interpreted to include liquefied gas as well as gas in gas phase.
According to an example embodiment, the gas tank may be a pressurized gas tank. A pressurized gas tank, or a pressure vessel, is advantageous since it can store high-pressure gas which is suitable for propelling, the dual fuel internal combustion engine.
According torn example embodiment, the first fuel separation arrangement may be positioned at an upper level of the fuel tank.
As described above, the upper level of the fuel tank should be understood as an upper position of the fuel tank as seen in the vertical direction of the vehicle when the vehicle is standing on a relatively horizontal surface. Hence, the upper level of the fuel tank is not the upper position of the tank when the vehicle is standing/driving in an uphill or a downhill slope etc. Positioning the first fuel separation arrangement at the upper level of the fuel tank thus, ensures that combustible gas present in the fuel tank will be provided there through since it will rise towards the surface of the liquid fuel.
According to an example embodiment, the first fuel separation arrangement may comprise a cavity, at least one inlet through-hole between the cavity and the fuel tank, a return through-hole between the cavity and the fuel tank, and an outlet conduit in fluid communication with the outlet to the ambient environment.
When the mixture of liquid fuel and combustible gas enters the cavity of the first fuel separation arrangement through the at least one inlet through-hole, the mixture will be directed towards an inner surface of the cavity. Hereby, the velocity of the mixture will be reduced. Due to gravity, the relatively heavy liquid fuel will be directed downwards through the return through-hole back to the fuel tank while the combustible gas, which has a density lower than air, will rise and be directed through the outlet conduit. Accordingly, and as an example embodiment, the at least one inlet through-hole may be arranged at a position between the return through-hole and the outlet conduit, as seen in a vertical direction thereof. The outlet conduit is thus positioned above the return through-hole.
According to an example embodiment, a cross-sectional area of the at least one inlet through-hole may be smaller than a cross-sectional area of the cavity. An advantage is that the velocity of the mixture, of fuel and combustible gas will be reduced which will further ensure that the heavier liquid fuels will be directed downwards and back into the fuel tank.
According to an example embodiment, the fuel tank arrangement may comprise a second fuel separation arrangement positioned in fluid communication between the first fuel separation arrangement and the outlet to the ambient environment.
An advantage of using a second fuel separation arrangement is that it is further ensured that liquid fuels will not be leaked to the ambient environment. Hence, in the unlikely event that liquid fuel will be present as a mixture with combustible gas downstream the first fuel separation arrangement; the second fuel separation arrangement will further reduce the probability of liquid fuel leakage to the ambient environment thereof. A further advantage of the second fuel separation arrangement is that e.g. rain water from the ambient environment that has entered the second fuel separation arrangement will be separated and prevented from entering the fuel tank. The second fuel separation arrangement thus has a dual function of preventing liquid fuel from being directed to the ambient environment and rain water from the ambient environment from entering the fuel tank.
According to an example embodiment, the second fuel separation arrangement may comprise an inlet conduit and an outlet conduit arranged in fluid communication with each other. According to an example embodiment, the inlet conduit may be positioned relative to the outlet conduit with an angle between 65-115 degrees.
Hereby, the mixture of liquid fuel and combustible gas will be directed through the inlet conduit and hit the inner surface of the outlet conduit. Hereby, the velocity of the mixture will be reduced and the liquid fuel will be directed downwards to a drain tank, or the like, and the combustible gas will be directed upwards towards the ambient environment.
According to an example embodiment, a cross-sectional area of the inlet conduit of the second fuel separation arrangement may be smaller than a cross-sectional area of the outlet conduit of the second fuel separation arrangement. An advantage is that the velocity of the mixture of liquid fuel and combustible gas will be reduced when entering the outlet conduit, which will further ensure that the heavier liquid fuel will be directed downwards to e.g. a drain tank or back to the fuel tank.
According to an example embodiment, the fuel tank arrangement may comprise a conduit connected upstream the inlet conduit of the second fuel separation arrangement, wherein the conduit and the inlet conduit of the second fuel separation arrangement are arranged approximately perpendicular relative to each other.
Hereby, a further position is provided where the velocity of the mixture of liquid fuel and combustible gas can be reduced. This is due to the fact that the mixture will hit the inner surface of the inlet conduit. The wording “perpendicular” should be understood to include normal tolerances.
According to an example embodiment, the fuel tank arrangement may comprise a pressure relief valve positioned downstream the first fuel separation arrangement.
An advantage of the pressure relief valve is that a safety device is provided for the fuel tank such that the pressure in the fuel tank will be kept at acceptable levels. Hence, the risk of bursting the fuel tank is reduced.
According to an example embodiment, the outlet to the ambient environment may be positioned at a level vertically above a vehicle compartment of a vehicle to which the fuel tank arrangement is mounted. As described above, an advantage is that the combustible gas will be vented to the ambient environment at a position which, people will not be able to inhale them. Since the density of the combustible gas is lower than air, the combustible gas will thus rise from this relatively high position.
According to a second aspect of the present invention, there is provided a vehicle comprising a dual fuel internal combustion engine for propulsion thereof, wherein the vehicle comprises a fuel tank arrangement according to any one of the above described example embodiments of the first aspect of the present invention.
Effects and features of this second aspect are largely analogous to those described above in relation to the first aspect of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.